Mask ROM device, semiconductor device including the mask ROM device, and methods of fabricating mask ROM device and semiconductor device

ABSTRACT

A mask read-only memory (ROM) device, which can stably output data, includes an on-cell and an off-cell. The on-cell includes an on-cell gate structure on a substrate and an on-cell junction structure within the substrate. The off-cell includes an off-cell gate structure on the substrate and an off-cell junction structure within the substrate. The on-cell gate structure includes an on-cell gate insulating film, an on-cell gate electrode and an on-cell gate spacer. The on-cell junction structure includes first and second on-cell ion implantation regions of a first polarity and third and fourth on-cell ion implantation regions of a second polarity. The off-cell gate structure includes an off-cell gate insulating film, an off-cell gate electrode and an off-cell gate spacer. The off-cell junction structure includes first and second off-cell ion implantation regions of the first polarity and a third off-cell ion implantation region of the second polarity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No. 12/132,148 filed on Jun. 3, 2008 now U.S. Pat. No. 7,777,256, which claims priority to Korean Patent Application No. 10-2007-0057484, filed on Jun. 12, 2007, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties.

This application claims the benefit of foreign priority to Korean Patent Application No. 10-2007-0057484 filed on Jun. 12, 2007, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of Invention

Embodiments of the present invention relate generally to mask read-only-memory (ROM) devices, semiconductor devices including mask ROM devices and methods of fabricating the mask ROM devices and semiconductor device including the same. More particularly, embodiments of the present invention relate to a mask ROM device including a cell junction, which has ion implantation regions of opposite polarities and thus enables an on-cell and an off-cell to operate stably, a semiconductor device including such a mask ROM device, and methods of fabricating the mask ROM device and the semiconductor device.

2. Description of the Related Art

Mask read-only-memory (ROM) devices are read-only semiconductor memory devices to which data cannot be written. A mask ROM device includes an on-cell and an off-cell. When activated, the on-cell remains on so that electric current can be transmitted from a source region to a drain region. On the other hand, the off-cell does not transmit electric current and remains off. Each cell has a transistor structure.

The term “on-cell” refers to a cell having a transistor structure in which a channel is formed in response to an activation voltage applied to a gate electrode and thus electric current is transmitted through the channel. The term “off-cell” refers to a cell having a transistor structure in which no channel is formed and thus electric current is not transmitted. When fabricated, the mask ROM device stores predetermined data. For example, the on-cell denotes data 1, and the off-cell denotes data 0.

In the mask ROM device, it is particularly important for the off-cell to stably output data 0. Accordingly, it is important that no channel is formed—even when the activation voltage is applied to a gate electrode therein. For this reason, numerous methods of preventing the formation of a channel have been suggested. In one method, ions of a polarity opposite to that of a channel are implanted into a channel region in order to prevent the formation of the channel. However, as a design rule of gate electrodes is reduced, it can be very difficult to implant ions into the channel region.

As the channel regions into which ions are implanted are reduced, it becomes more difficult to form ion implantation mask patterns at precise locations. In addition, because ions penetrate through the gate electrode, high ion implantation energy is required. Therefore, a very thick ion implantation mask must be formed. Because a high concentration of ions of a polarity opposite to that of the channel are also implanted into a junction region, leakage current increases while a breakdown voltage is reduced.

SUMMARY

Embodiments exemplarily described herein can be characterized as capable of providing a mask read-only-memory (ROM) device in which a transistor of an on-cell can maintains low leakage current and a sufficiently high breakdown voltage and a transistor of an off-cell can stably output data because no channel is formed even when the transistor is activated. It will be appreciated, however, that features of embodiments exemplarily described herein are not restricted to the one set forth herein. The above and other features of embodiments exemplarily described herein will become more apparent to one of ordinary skill in the art to which the present invention pertains by referencing the detailed description below.

According to one embodiment, a mask ROM device can be generally characterized as including an on-cell and an off-cell. The on-cell may include an on-cell gate structure formed on a substrate and comprising an on-cell gate insulating film, an on-cell gate electrode, and an on-cell gate spacer; and an on-cell junction structure formed within the substrate and comprising first and second on-cell ion implantation regions of a first polarity and third and fourth on-cell ion implantation regions of a second polarity. The off-cell may include an off-cell gate structure formed on the substrate and comprising an off-cell gate insulating film, an off-cell gate electrode, and an off-cell gate spacer; and an off-cell junction structure formed within the substrate comprising first and second off-cell ion implantation regions of the first polarity and a third off-cell ion implantation region of the second polarity.

According to one embodiment, a method of fabricating a mask ROM device can be generally characterized as forming an on-cell gate insulating film and an off-cell gate insulating film on a substrate; forming an on-cell gate electrode on the on-cell gate insulating film; forming an off-cell gate electrode on the off-cell gate insulating film; performing a first ion implantation process and a second ion implantation process using ions of a first polarity to form a first on-cell ion implantation region, a first off-cell ion implantation region, a second on-cell ion implantation region and a second off-cell ion implantation region, wherein the first and second on-cell ion implantation regions are aligned with a side surface of the on-cell gate electrode and wherein the first and second off-cell ion implantation regions are aligned with a side surface of the off-cell gate electrode; performing a third ion implantation process using ions of a second polarity to form a third on-cell ion implantation region that is aligned with the side surfaces of the on-cell gate electrode and the off-cell gate electrode; forming gate spacers on the side surfaces of the on-cell gate electrode and the off-cell gate electrode; and performing a fourth ion implantation process to form a fourth on-cell ion implantation region and a third off-cell ion implantation region that are aligned with the gate spacers.

According to one embodiment, a semiconductor device can be generally characterized as comprising a mask ROM device and a CMOS. The mask ROM device may include an on-cell comprising an on-cell gate structure formed on a first region of the substrate and an on-cell junction structure formed within the first region of the substrate; and an off-cell comprising an off-cell gate structure formed on the first region of the substrate and an off-cell junction structure formed within the first region of the substrate. The CMOS may include a PMOS gate structure comprising a PMOS gate insulating film, a PMOS gate electrode and a PMOS gate spacer formed on a second region of the substrate; a PMOS structure comprising a P-type ion implantation region formed within the second region of the substrate; an NMOS gate structure comprising an NMOS gate insulating film, an NMOS gate electrode and an NMOS gate spacer formed on the second region of the substrate; and an NMOS structure comprising an N-type ion implantation region formed within the second region of the substrate. The on-cell gate structure may include an on-cell gate insulating film, an on-cell gate electrode and an on-cell gate spacer. The on-cell junction structure may include first and second on-cell ion implantation regions of a first polarity and third and fourth on-cell ion implantation regions of a second polarity. The off-cell gate structure may include an off-cell gate insulating film, an off-cell gate electrode and an off-cell gate spacer formed on the first region of the substrate. The off-cell junction structure may include first and second off-cell ion implantation regions of the first polarity and a third off-cell ion implantation region of the second polarity.

According to one embodiment, a method of fabricating a semiconductor device can be generally characterized as forming an on-cell gate insulating film and an off-cell gate insulating film on a first region of a substrate and forming a CMOS gate insulating film on a second region of the substrate; forming an on-cell gate electrode on the on-cell gate insulating film; forming an off-cell gate electrode on the off-cell gate insulating film; forming an NMOS gate electrode and a PMOS gate electrode on the CMOS gate insulating film; performing a first ion implantation process and a second ion implantation process using ions of a first polarity to form a first on-cell ion implantation region, a first off-cell ion implantation region, a second on-cell ion implantation region and a second off-cell ion implantation region that are aligned with side surfaces of the on-cell gate electrode and the off-cell gate electrode; performing a third ion implantation process using ions of a second polarity to form a third on-cell ion implantation region and a first NMOS ion implantation region that are aligned with side surfaces of the on-cell gate electrode and the NMOS gate electrode, respectively; performing a fourth ion implantation process using ions of the first polarity to form a first PMOS ion implantation region that is aligned with a side surface of the PMOS gate electrode; forming an on-cell gate spacer, an off-cell gate spacer, an NMOS gate spacer and a PMOS gate spacer on the side surfaces of the on-cell and off-cell gate electrodes and the NMOS and PMOS gate electrodes, respectively; performing a fifth ion implantation process using ions of the second polarity to form a fourth on-cell ion implantation region, a third off-cell ion implantation region and a second NMOS ion implantation region that are aligned with the on-cell gate spacer, the off-cell gate spacer and the NMOS gate spacer, respectively; and performing a sixth ion implantation region using ions of the first polarity to form a second PMOS ion implantation region that is aligned with the PMOS gate spacer.

Other embodiments of the present invention are included in the following detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the embodiments exemplarily described above will become more apparent by describing in detail embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a schematic diagram illustrating a mask ROM device according to an exemplary embodiment;

FIGS. 2A and 2B are enlarged views of an on-cell gate structure and an on-cell junction structure of an on-cell and an off-cell gate structure and an off-cell junction structure of an off-cell, exemplarily illustrated in FIG. 1;

FIG. 3 is a schematic diagram illustrating a mask ROM device according to another exemplary embodiment;

FIGS. 4A and 4B are enlarged views of an on-cell gate structure and an on-cell junction structure of an on-cell and an off-cell gate structure and an off-cell junction structure of an off-cell, exemplarily illustrated in FIG. 3;

FIGS. 5A through 5F illustrate one embodiment of an exemplary method of forming a gate structure and a junction structure of a mask ROM device; and

FIGS. 6A through 6I illustrate one embodiment of an exemplary method of forming a semiconductor device including a mask ROM device.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention will now be described more fully with reference to the accompanying drawings. These embodiments may, however, be realized in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, sizes and relative sizes of the layers and regions are exaggerated for clarity. Like reference numerals in the drawings denote like elements, and thus their description will be omitted.

Exemplary embodiments of the present invention are described herein with reference to cross-sectional illustrations representing idealized embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments of the invention should not be construed as limited to the particular shapes of regions illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the actual shape of a region of a device and are not intended to limit the scope of the invention as defined in the claims.

As used herein, the term “N-type ion” may refer to an ionized element that belongs to group V of a periodic table, such as phosphorous (P) or arsenic (As). In addition, the term “P-type ion” may refer to an ionized element that belongs to group III of the periodic table, such as boron (B) or boron tri-fluoride (BF₃).

As used herein, the terms “high concentration” and “low concentration” refer to relative concentrations based on a comparison of two concentrations and does not necessarily refer to a preset concentration.

Hereinafter, a mask ROM device and a method of fabricating the same according to one exemplary embodiment will be described in detail with reference to the attached drawings.

FIG. 1 is a schematic diagram illustrating a mask ROM device 100 according to an exemplary embodiment.

Referring to FIG. 1, the mask ROM device 100 includes an on-cell 110 a and an off-cell 110 b. The on-cell 110 a includes an on-cell gate structure 130 a and an on-cell junction structure 140 a on a substrate 120. The off-cell 110 b includes an off-cell gate structure 130 b and an off-cell junction structure 140 b on the substrate 120.

The on-cell junction structure 140 a of the on-cell 110 a and the off-cell junction structure 140 b of the off-cell 110 b include ion implantation regions having various polarities, concentrations and shapes. Each ion implantation region of the on-cell junction structure 140 a and the off-cell junction structure 140 b is exemplarily illustrated in FIG. 1 as if it had an independent shape. However, the ion implantation regions may actually appear to be a single ion implantation region due to diffusion and recombination. In addition, a boundary line or interface of each ion implantation region illustrated in FIG. 1 is exemplary and may be modified to various shapes, which will be described in greater detail below.

FIGS. 2A and 2B are enlarged views of the on-cell gate structure 130 a and the on-cell junction structure 140 a of the on-cell 110 a and the off-cell gate structure 130 b and the off-cell junction structure 140 b of the off-cell 110 b exemplarily illustrated in FIG. 1.

FIG. 2A is a schematic diagram illustrating the on-cell gate structure 130 a and the on-cell junction structure 140 a of the on-cell 110 a.

Referring to FIG. 2A, the on-cell 110 a includes the on-cell gate structure 130 a and the on-cell junction structure 140 a.

The on-cell gate structure 130 a includes an on-cell gate insulating film 131 a, an on-cell gate electrode 133 a, an on-cell gate capping layer 135 a, an on-cell gate sidewall 137 a, and an on-cell gate spacer 139 a.

The on-cell junction structure 140 a includes a first on-cell ion implantation region 143 a, a second on-cell ion implantation region 145 a, and a third on-cell ion implantation region 147 a.

The on-cell gate insulating film 131 a, the on-cell gate electrode 133 a, the on-cell gate capping layer 135 a, the on-cell gate sidewall 137 a, and the on-cell gate spacer 139 a in the on-cell gate structure 130 a function as a gate insulating film, a gate electrode, a gate capping layer, a gate sidewall, and a gate spacer, respectively.

Each of the on-cell gate insulating film 131 a, the on-cell gate electrode 133 a, the on-cell gate capping layer 135 a and the on-cell gate sidewall 137 a may include a material such as silicon oxide. In one embodiment, each of the on-cell gate insulating film 131 a, the on-cell gate electrode 133 a, the on-cell gate capping layer 135 a and the on-cell gate sidewall 137 a may be formed of a silicon oxide film. The on-cell gate spacer 139 a may include a material such as silicon nitride, silicon oxynitride, or the like or a combination thereof. In one embodiment, the on-cell gate spacer 139 a may be formed of a silicon nitride film. It will be appreciated, however, that the materials and films of the various structures is not necessarily limited thereto. For example, a combination of various insulating materials and/or films of insulating materials such as aluminum oxide, hafnium oxide, silicon oxynitride or the like may also be used in addition to, or in place of, silicon oxide.

A method of forming the on-cell gate insulating film 131 a, the on-cell gate electrode 133 a, the on-cell gate capping layer 135 a, the on-cell gate sidewall 137 a, and the on-cell gate spacer 139 a will be described in greater detail below.

The polarity of the first on-cell ion implantation region 143 a may be opposite to that of a channel. For example, if the channel is of an N-type, the first on-cell ion implantation region 143 a may be of a P-type. Conversely, if the channel is of the P-type, the first on-cell ion implantation region 143 a may be of the N-type. Because an N-type channel is formed in an NMOS, the first on-cell ion implantation region 143 may be formed by implanting P-type ions. Because a P-type channel is formed in a PMOS, the first on-cell ion implantation region 143 may be formed by implanting N-type ions.

The first on-cell ion implantation region 143 a may extend to a point under the on-cell gate electrode 133 a. Accordingly, the first on-cell ion implantation region 143 a may extend further under the on-cell gate electrode 133 a than the second and third on-cell ion implantation regions 145 a and 147 a in a horizontal direction. Because the polarity of the first on-cell ion implantation region 143 a is opposite to that of the channel, the first on-cell ion implantation region 143 a can, in one embodiment, prevent a short-channel effect. That is, the first on-cell ion implantation region 143 a can prevent more junction extension than is necessary. In this case, the first on-cell ion implantation region 143 a may perform the function of a halo or a pocket well.

In one embodiment, the polarity of the second on-cell ion implantation region 145 a may be identical to that of the channel. The second on-cell ion implantation region 145 a may have a relatively lower concentration of ions than the third on-cell ion implantation region 147 a. In addition, the second on-cell ion implantation region 145 a may be the shallowest among the first through third on-cell ion implantation regions 143 a through 147 a. In a junction structure known as a lightly doped drain (LDD), the second on-cell ion implantation region 145 a may be formed by implanting ions to a low concentration.

In one embodiment, the polarity of the third on-cell ion implantation region 147 a may be identical to that of the channel. The third on-cell ion implantation region 147 a may have a relatively higher concentration of ions than the second on-cell ion implantation region 145 a. In one embodiment, the third on-cell ion implantation region 147 a may be the deepest among the first through third on-cell ion implantation regions 143 a through 147 a. In another embodiment, however, the first on-cell ion implantation region 143 a may be formed deeper than the third on-cell ion implantation region 147 a. In the junction structure known as the LDD, the third on-cell ion implantation region 147 a may be formed by implanting ions to a high concentration.

A method of forming the first through third on-cell ion implantation regions 143 a through 147 a will be described in greater detail below.

When the on-cell 110 a is activated in response to an activation voltage, which is applied to the on-cell gate electrode 133 a, a channel is formed and electric current is transmitted through the channel. Thus, when the on-cell 110 a is activated, the on-cell 110 a outputs data 1.

FIG. 2B is a schematic diagram illustrating the off-cell gate structure 130 b and the off-cell junction structure 140 b of the off-cell 110 b.

Referring to FIG. 2 b, the off-cell 110 b includes the off-cell gate structure 130 b and the off-cell junction structure 140 b.

The off-cell gate structure 130 b includes an off-cell gate insulating film 131 b, an off-cell gate electrode 133 b, an off-cell gate capping layer 135 b, an off-cell gate sidewall 137 b, and an off-cell gate spacer 139 b.

The off-cell junction structure 140 b includes a first off-cell ion implantation region 143 b and a second off-cell ion implantation region 145 b.

The off-cell gate insulating film 131 b, the off-cell gate electrode 133 b, the off-cell gate capping layer 135 b, the off-cell gate sidewall 137 b, and the off-cell gate spacer 139 b may be formed at the same time as the on-cell gate insulating film 131 a, the on-cell gate electrode 133 a, the on-cell gate capping layer 135 a, the on-cell gate sidewall 137 a, and the on-cell gate spacer 139 a. In addition, the off-cell gate insulating film 131 b, the off-cell gate electrode 133 b, the off-cell gate capping layer 135 b, the off-cell gate sidewall 137 b, and the off-cell gate spacer 139 b may perform the same transistor functions as the on-cell gate insulating film 131 a, the on-cell gate electrode 133 a, the on-cell gate capping layer 135 a, the on-cell gate sidewall 137 a, and the on-cell gate spacer 139 a.

The on-cell gate structure 130 a illustrated in FIG. 2A and the off-cell gate structure 130 b illustrated in FIG. 2B may be formed simultaneously, which will be described in greater detail below.

The first off-cell ion implantation region 143 b may be formed by implanting ions of the same polarity as that of the first on-cell ion implantation region 143 a. In addition, the first off-cell ion implantation region 143 b and the first on-cell ion implantation region 143 a may be formed simultaneously, which will be described in greater detail below. The first off-cell ion implantation region 143 b may extend to a point under the off-cell gate electrode 133 b. Accordingly, the first off-cell ion implantation region 143 b may extend further under the off-cell gate electrode 133 b than the second off-cell ion implantation region 147 b in a horizontal direction.

In one embodiment, the second off-cell ion implantation region 147 b may be formed by implanting ions of the same polarity as that of the third on-cell ion implantation region 147 a. In addition, the second off-cell ion implantation region 147 b and the third on-cell ion implantation region 147 a may be formed simultaneously, which will be described in greater detail below. In one embodiment, the second off-cell ion implantation region 147 b may be formed deeper than the first off-cell ion implantation region 143 b. In another embodiment, however, the first off-cell ion implantation region 143 b may be formed deeper than the second off-cell ion implantation region 147 b.

The off-cell 110 b) does not have an ion implantation region (corresponding to the second on-cell ion implantation region 145 a of FIG. 2A) in which a channel to the on-cell 110 a can be formed. Therefore, even if the activation voltage is applied to the gate electrode 133 b, no channel is formed. Because electric current is not transmitted, the off-cell 110 b always outputs data 0 (zero).

FIG. 3 is a schematic diagram illustrating a mask ROM device 200 according to another exemplary embodiment.

Referring to FIG. 3, the mask ROM device 200 includes an on-cell 210 a and an off cell 210 b. The on-cell 210 a includes an on-cell gate structure 230 a and an on-cell junction structure 240 a on a substrate 220. The off-cell 210 b includes an off-cell gate structure 230 b and an off-cell junction structure 240 b on the substrate 220.

In one embodiment, the on-cell junction structure 240 a of the on-cell 210 a and the off-cell junction structure 240 b of the off-cell 210 b include ion implantation regions having various polarities and concentrations. Each ion implantation region of the on-cell junction structure 240 a and the off-cell junction structure 240 b is illustrated in FIG. 3 as if it had an independent shape. However, the ion implantation regions may actually appear to be a single ion implantation region due to diffusion and recombination. In addition, a boundary line or interface of each ion implantation region illustrated in FIG. 3 is exemplary and may be modified to various shapes, which will be described in greater detail below.

The on-cell junction structure 240 a and the off-cell junction structure 240 b of the mask ROM device illustrated in FIG. 3 may be more elaborate than those of the mask ROM device illustrated in FIG. 1. For example, while ion implantation regions into which ions of a polarity opposite to that of a channel are implanted are formed as a wide region in the mask ROM device 100 shown in FIG. 1, they are formed as two regions in the mask ROM device 200 shown in FIG. 3. Each ion implantation region can be formed in two step ion implantation processes, and the position of each ion implantation region is not necessarily distinguished, which will be described in greater detail below.

FIGS. 4A and 4B are enlarged views of the on-cell gate structure 230 a and the on-cell junction structure 240 a of the on-cell 210 a and the off-cell gate structure 230 b and the off-cell junction structure 240 b of the off-cell 210 b exemplarily illustrated in FIG. 3.

FIG. 4A is a schematic diagram illustrating the on-cell gate structure 230 a and the on-cell junction structure 240 a of the on-cell 210 a.

Referring to FIG. 4A, the on-cell 210 a includes the on-cell gate structure 230 a and the on-cell junction structure 240 a.

The on-cell gate structure 230 a includes an on-cell gate insulating film 231 a, an on-cell gate electrode 233 a, an on-cell gate capping layer 235 a, an on-cell gate sidewall 237 a, and an on-cell gate spacer 239 a.

The on-cell junction structure 240 a includes a first on-cell ion implantation region 241 a, a second on-cell ion implantation region 243 a, a third on-cell ion implantation region 245 a, and a fourth on-cell ion implantation region 247 a.

The on-cell gate insulating film 231 a, the on-cell gate electrode 233 a, the on-cell gate capping layer 235 a, the on-cell gate sidewall 237 a, and the on-cell gate spacer 239 a in the on-cell gate structure 230 a function as a gate insulating film, a gate electrode, a gate capping layer, a gate sidewall, and a gate spacer, respectively.

Each of the on-cell gate insulating film 231 a, the on-cell gate electrode 233 a, the on-cell gate capping layer 235 a and the on-cell gate sidewall 237 a may include a material such as silicon oxide. In one embodiment, each of the on-cell gate insulating film 231 a, the on-cell gate electrode 233 a, the on-cell gate capping layer 235 a and the on-cell gate sidewall 237 a may be formed of a silicon oxide film. The on-cell gate spacer 239 a may include a material such as silicon nitride, silicon oxynitride, or the like of a combination thereof. In one embodiment, the on-cell gate spacer 239 a may be formed of a silicon nitride film. It will be appreciated, however, that the materials and films of the various structures is not necessarily limited thereto. For example, a combination of various insulating materials and/or films of insulating materials such as aluminum oxide, hafnium oxide, and silicon oxynitride, or the like may also be used in addition to, or in place of, silicon oxide.

A method of forming the on-cell gate insulating film 231 a, the on-cell gate electrode 233 a, the on-cell gate capping layer 235 a, the on-cell gate sidewall 237 a, and the on-cell gate spacer 239 a will be described in greater detail below.

The polarity of the first on-cell ion implantation region 241 a and that of the second on-cell ion implantation region 243 a may be opposite to that of a channel. For example, if the channel is of the N-type, the first on-cell ion implantation region 241 a and the second on-cell ion implantation region 243 a may be of the P-type. Conversely, if the channel is of the P-type, the first on-cell ion implantation region 241 a and the second on-cell ion implantation region 243 a may be of the N-type.

The second on-cell ion implantation region 243 a may extend to a point under the on-cell gate electrode 233 a. Accordingly, the second on-cell ion implantation region 243 a may extend further than the first, third and fourth on-cell ion implantation regions 241 a, 245 a and 247 a under the on-cell gate electrode 233 a in a horizontal direction. Because the polarity of the second on-cell ion implantation region 243 a is opposite to that of the channel, the second on-cell ion implantation region 243 a can prevent the short-channel effect. In this case, the second on-cell ion implantation region 243 a may perform the function of a halo or a pocket well.

The second on-cell ion implantation region 243 a may surround the first on-cell ion implantation region 241 a.

In one embodiment, the polarity of the third on-cell ion implantation region 245 a may be identical to that of the channel. The third on-cell ion implantation region 245 a may have a relatively lower concentration of ions than the fourth on-cell ion implantation region 247 a. In addition, the third on-cell ion implantation region 245 a may be the shallowest among the first through fourth on-cell ion implantation regions 241 a through 247 a. In the junction structure known as the LDD, the third on-cell ion implantation region 245 a may be formed by implanting ions to a low concentration.

In one embodiment, the polarity of the fourth on-cell ion implantation region 247 a may be identical to that of the channel. The fourth on-cell ion implantation region 247 a may have a relatively higher concentration of ions than the third on-cell ion implantation region 245 a. In one embodiment, the fourth on-cell ion implantation region 247 a may be the deepest among the first through fourth on-cell ion implantation regions 241 a through 247 a. In another embodiment, however, the second on-cell ion implantation region 243 a may be formed deeper than the fourth on-cell ion implantation region 247 a. In the junction structure known as the LDD, the fourth on-cell ion implantation region 247 a may be formed by implanting ions to a high concentration.

A method of forming the first through fourth on-cell ion implantation regions 241 a through 247 a will be described in greater detail below.

When the on-cell 210 a is activated in response to the activation voltage, which is applied to the on-cell gate electrode 233 a, a channel is formed and electric current is transmitted through the channel. Thus, when the on-cell 210 a is activated, the on-cell 210 a outputs data 1.

FIG. 4B is a schematic diagram illustrating the off-cell gate structure 230 b and the off-cell junction structure 240 b of the off-cell 210 b. Referring to FIG. 4 b, the off-cell 210 b includes the off-cell gate structure 230 b and the off-cell junction structure 240 b.

The off-cell gate structure 230 b includes an off-cell gate insulating film 231 b, an off-cell gate electrode 233 b, an off-cell gate capping layer 235 b, an off-cell gate sidewall 237 b, and an off-cell gate spacer 239 b.

The off-cell junction structure 240 b includes a first off-cell ion implantation region 241 b, a second off-cell ion implantation region 243 b, and a third off-cell ion implantation region 247 b.

The off-cell gate insulating film 231 b, the off-cell gate electrode 233 b, the off-cell gate capping layer 235 b, the off-cell gate sidewall 237 b, and the off-cell gate spacer 239 b may be formed at the same time as the on-cell gate insulating film 231 a, the on-cell gate electrode 233 a, the on-cell gate capping layer 235 a, the on-cell gate sidewall 237 a, and the on-cell gate spacer 239 a. In addition, the off-cell gate insulating film 231 b, the off-cell gate electrode 233 b, the off-cell gate capping layer 235 b, the off-cell gate sidewall 237 b, and the off-cell gate spacer 239 b may perform the same transistor functions as the on-cell gate insulating film 231 a, the on-cell gate electrode 233 a, the on-cell gate capping layer 235 a, the on-cell gate sidewall 237 a, and the on-cell gate spacer 239 a.

The off-cell gate structure 230 a illustrated in FIG. 4A and the off-cell gate structure 230 b illustrated in FIG. 4B may be formed simultaneously, and thus a detailed description thereof will be omitted.

The first off-cell ion implantation region 241 b and the second off-cell ion implantation region 243 b may be formed by implanting ions with the same polarities with those of the first on-cell ion implantation region 241 a and the second on-cell ion implantation region 243 a. The second off-cell ion implantation region 243 b may extend to a point under the off-cell gate electrode 233 b. Accordingly, the second off-cell ion implantation region 243 b may extend further under the off-cell gate electrode 233 b than the third off-cell ion implantation region 247 b in a horizontal direction.

The second off-cell in implantation region 243 b may surround the first off-cell ion implantation region 241 b.

In one embodiment, the polarity of the third off-cell ion implantation region 247 b may be identical to that of the fourth on-cell ion implantation region 247 a. In addition, the third off-cell ion implantation region 247 b and the fourth on-cell ion implantation region 247 a may be formed simultaneously. In one embodiment, the third off-cell ion implantation region 247 b may be formed deeper than the second off-cell ion implantation region 243 b. In another embodiment, however, the second off-cell ion implantation region 243 b may be formed deeper than the third off-cell ion implantation region 247 b.

The off-cell 210 b does not have an ion implantation region (corresponding to the first on-cell ion implantation region 245 a of FIG. 4A) in which a channel to the on-cell 210 a can be formed. Therefore, even if the activation voltage is applied to the gate electrode 233 b, no channel is formed. Because electric current is not transmitted, the off-cell 210 b always outputs data 0 (zero).

A method of forming the first through third off-cell ion implantation regions 241 b, 243 b and 247 b will be described in greater detail below.

Hereinafter, an exemplary embodiment method of forming a gate structure and a junction structure of a mask ROM device will be described with reference to FIGS. 5A through 5F.

FIGS. 5A through 5F may not exactly match FIGS. 1 through 4B illustrating the mask ROM devices 100 and 200 described above because a description of a heat-treatment process, which accompanies an ion implantation process, is omitted in order to promote the understanding of the technical spirit of the concepts described herein. After the heat-treatment process, ion implantation regions are diffused. However, the heat-treatment process is not illustrated in FIGS. 5A through 5F. Nevertheless, it should be understood that the heat-treatment process is not omitted. For example, the heat-treatment process may be performed after every implantation process or after every two or more ion implantation processes.

Referring to FIG. 5A, an on-cell gate structure 310 a and an off-cell gate structure 310 b, each of which does not have a spacer, are formed on a substrate 320.

The on-cell gate structure 310 a includes an on-cell gate insulating film 331 a′, an on-cell gate electrode 333 a, an on-cell gate capping layer 335 a and an on-cell gate sidewall 337 a. The off-cell gate structure 310 b includes an off-cell gate insulating film 331 b, an off-cell gate electrode 333 b, an off-cell gate capping layer 335 b and an off-cell gate sidewall 337 b. The on-cell gate structure 310 a′ and the off-cell gate structure 310 b′ may be formed simultaneously.

Each of the on-cell gate insulating film 331 a′ and the off-cell gate insulating film 331 b′ may include a material such as silicon oxide, aluminum oxide, hafnium oxide, or the like or a combination thereof. In one embodiment, each of the on-cell gate insulating film 331 a′ and the off-cell gate insulating film 331 b′ may be formed of a silicon oxide film, an aluminum oxide film, a hafnium oxide film or the like or a combination thereof. In embodiments where the on-cell gate insulating film 331 a′ and the off-cell gate insulating film 331 b′ are formed of a silicon oxide film, the silicon substrate 320 may be oxidized or a silicon oxide film may be deposited on the silicon substrate 320 to form each of the on-cell gate insulating film 331 a′ and the off-cell gate insulating film 331 b′. When each of the on-cell gate insulating film 331 a′ and the off-cell gate insulating film 331 b′ is formed by depositing the silicon oxide film, a chemical vapor deposition (CVD) method, an atomic layer deposition (ALD) method, or the like may be used. When each of the on-cell gate insulating film 331 a′ and the off-cell gate insulating film 331 b′ is formed of an insulating film other than the silicon oxide film, an appropriate deposition method may be used.

Each of the on-cell gate electrode 333 a and the off-cell gate electrode 333 b comprises a conductive material and may be a single layer or a multi-layer including polycrystalline silicon, metal-silicide, one or more metal compounds, or one or more metals.

The on-cell gate capping layer 335 a and off-cell gate capping layers 335 b and the on-cell gate sidewalls 337 a and off-cell gate sidewalls 337 b are formed on top and side surfaces of the on-cell gate electrode 333 a and off-cell gate electrodes 333 b, respectively, thereby protecting the on-cell and off-cell gate electrodes 333 a and 333 b from physical damage and chemical reactions.

The on-cell gate insulating film 331 a′ and the off-cell gate insulating film 331 b′ may function as buffers when ions are implanted into the substrate 320.

Referring to FIG. 5B, a first ion implantation process is performed on a whole surface of the substrate 320 to form first ion implantation regions 341 a′ and 341 b′ in the substrate 320.

The first ion implantation regions 341 a′ and 341 b′ may be formed by implanting ions of an opposite polarity to that of a channel. For example, in the case of an NMOS transistor having an N-type channel, the first ion implantation regions 341 a′ and 341 b′ may be formed by implanting P-type ions. In the case of a PMOS transistor having a P-type channel, the first ion implantation regions 341 a′ and 341 b′ may be formed by implanting N-type ions.

The first ion implantation regions 341 a′ and 341 b′ may be formed using the on-cell gate structure 310 a′ and off-cell gate structure 310 b′ as ion implantation masks. Therefore, the first ion implantation regions 341 a′ and 341 b′ may be aligned with side surfaces of the on-cell gate structure 310 a′ and off-cell gate structure 310 b′, respectively (e.g. side ends of the on-cell gate electrode, off-cell gate electrode, the on-cell gate sidewalls and/or the sidewall of the off-cell gate sidewalls). However, after the first ion implantation regions 341 a′ and 341 b′ are heat-treated, they may extend under the on-cell gate structure 310 a′ and off-cell gate structure 310 b.

In one embodiment, the first ion implantation regions 341 a′ and 341 b′ may be formed by implanting BF₂ ⁺ ions. For example, the first ion implantation regions 341 a′ and 341 b′ may be formed by perpendicularly implanting the BF₂ ⁺ ions into a surface of the substrate 320 to an ion concentration of approximately 4E13 and at an ion acceleration energy of approximately 30 KeV. In this case, the first ion implantation regions 341 a′ and 341 b′ may be formed to a depth of approximately 200 to 300 nm. It will be appreciated, however, that this range is a mere example, and the present invention is not limited thereto. That is, the depths of the first ion implantation regions 341 a′ and 341 b′ may vary.

Referring to FIG. 5C, a second ion implantation process is performed on the whole surface of the substrate 320 to form second ion implantation regions 343 a′ and 343 b′ in the substrate 320.

The second ion implantation regions 343 a′ and 343 b′ may be formed by implanting ions of the same polarity as that of the first ion implantation regions 341 a′ and 341 b′. For example, the second ion implantation regions 343 a′ and 343 b′ may be formed by implanting B⁺ ions into the substrate 320 to an ion concentration of approximately 4E13 and at an ion acceleration energy of approximately 30 KeV. In this case, the second ion implantation process may be an angled process. That is, ions are not implanted in a direction perpendicular to the surface of the substrate 320. Instead, as illustrated in FIG. 5C, the ions are implanted into the substrate 320 at a predetermined angle with respect to the surface of the substrate 320 to form the second ion implantation regions 343 a′ and 343 b′. In one embodiment, the predetermined angle is approximately 0 to 45 degrees. In another embodiment, the predetermined angle is approximately 30 degrees.

With the same ion implantation energy, B⁺ ions can be implanted deeper than BF₂ ⁺ ions as illustrated in FIG. 5C. It is generally known that B⁺ ions can be implanted approximately five times deeper than BF₂ ⁺ ions.

Referring to FIG. 5D, an ion implantation mask M is formed on the off-cell gate structure 310 b) to prevent the implantation of ions into the off-cell gate structure 310 b). Then, a third ion implantation process is performed to form third ion implantation regions 345 a′. The third ion implantation regions 345 a′ may be aligned with the side ends of the on-cell gate structure 310 a′.

The polarity of the third ion implantation regions 345 a′ may be identical to that of the channel. Accordingly, the polarity of the third ion implantation regions 345 a′ may be opposite to the polarity of the first and second ion implantation regions 341 a, 341 b, 343 a, and 343 b.

In addition, the third ion implantation regions 345 a′ may have a high concentration of ions in an LDD junction structure. In one embodiment, the third ion implantation regions 345 a′ may be formed by implanting phosphorous (P), arsenic (As) or the like or a combination thereof.

In one embodiment, the third ion implantation regions 345 a′ may be shallower than the first ion implantation region 341 a. It will be appreciated, however, that the third ion implantation regions 345 a′ may, alternatively, not be shallower than the first ion implantation region 341 a.

Referring to FIG. 5E, the on-cell gate spacers 339 a and off-cell gate spacers 339 b are formed on side surfaces of the on-cell gate electrodes 333 a and off-cell gate electrodes 333 b and the on-cell gate sidewalls 337 a and off-cell gate sidewalls 337 b, respectively.

Each of the on-cell gate spacers 339 a and off-cell gate spacers 339 b may include a material such as silicon nitride, silicon oxynitride, or the like or a combination thereof. In one embodiment, each of the on-cell gate spacers 339 a and off-cell gate spacers 339 b may be formed of a silicon nitride film, a silicon oxy-nitride film, or the like or a combination thereof. In one embodiment, each of the on-cell gate spacers 339 a and off-cell gate spacers 339 b may be formed by forming an insulating film over the entire substrate 320 (e.g., on the on-cell gate insulating film 331 a′, off-cell gate insulating film 331 b′, on-cell gate capping layer 335 a, off-cell gate capping layer, on-cell gate sidewalls 337 a, and off-cell gate sidewalls 337 b) followed by anisotropically etching the insulating film. Since the anisotropic etching method is a well-known technology, a detailed description thereof will be omitted.

Referring to FIG. 5F, a fourth ion implantation process is performed to form fourth ion implantation regions 347 a′ and 347 b′.

The fourth ion implantation regions 347 a′ and 347 b′ may be formed using the on-cell gate structure 310 a′ and off-cell gate structure 310 b′, which include the on-cell gate spacers 339 a and off-cell gate spacers 339 b, respectively, as ion implantation masks. Therefore, the fourth ion implantation regions 347 a′ and 347 b′ may be aligned with the on-cell gate spacers 339 a and off-cell gate spacers 339 b, respectively. It will be appreciated, however, that the fourth ion implantation regions 347 a′ and 347 b′ may not be aligned with the on-cell gate spacers 339 a and off-cell gate spacers 339 b, respectively, because the fourth ion implantation regions 347 a′ and 347 b′ may expand after a heat-treatment process.

An exemplary embodiment of a method of fabricating a mask ROM device together with a semiconductor device (e.g., a logic device) will now be described with respect to FIGS. 6A through 6I.

FIGS. 6A through 6I illustrate one embodiment of an exemplary method of forming a semiconductor device including a mask ROM device.

For purposes of discussion, the left half of each drawing represents a mask ROM region and the right half of each drawing represents a complementary metal oxide semiconductor (CMOS) region. The CMOS region may be a logic region, a region for another memory device, or the like. In addition, it is assumed that all transistors in the mask ROM region are NMOS transistors. It will be appreciated, however, that all transistors in the mask ROM region could also be PMOS transistors. For purposes of discussion, it is assumed that all ion implantation masks are photoresist patterns. It will be appreciated, however, that substantially any type of ion implantation mask could be used.

Referring to FIG. 6A, isolation regions 405, P-wells 410P, N-wells 410N, a gate insulating film 431′, and gate electrodes 433 a through 433 d are formed in the mask ROM region and the CMOS region.

In one embodiment, the isolation regions 405 are shallow trench isolation (STI) regions. Since methods of forming the STI regions and the P-well 410P and N-wells 410N are well known, detailed description thereof will be omitted.

The gate insulating film 431′ may comprise an insulating material such as silicon oxide, aluminum oxide, hafnium oxide, silicon oxynitride, or the like or a combination thereof. Each of the gate electrodes 433 a through 433 d may comprise a conductor such as silicon, metal silicide, metal, a metal compound, or the like or a combination thereof.

Since the materials and methods of forming the gate insulating film 431′ and the gate electrodes 433 a through 433 d are well known, a detailed description thereof will be omitted.

Referring to FIG. 6B, a first ion implantation mask M1 is formed on the CMOS region, and a first ion implantation process is performed on the mask ROM region. As a result, first ion implantation regions 441 a′ and 441 b′ are formed.

The first ion implantation regions 441 a′ and 441 b′ may be formed by implanting P-type ions.

In the first ion implantation process, BF₂ ⁺ ions may be implanted perpendicular to a surface of the substrate 420 to an ion concentration of approximately 4E13 and at an ion acceleration energy of approximately 30 KeV.

Referring to FIG. 6C, still using the first ion implantation mask M1, a second ion implantation process is performed. As a result, second ion implantation regions 443 a′ and 443 b′ are formed.

The second ion implantation regions 443 a′ and 443 b′ may be formed by implanting P-type ions.

In the second ion implantation process, B⁺ ions may be implanted to an ion concentration of approximately 4E13, at an ion acceleration energy of approximately 30 KeV, and at an angle of approximately 30 degrees with respect to the surface of the substrate 420. This process is called “angled ion implantation” and is well known to those of ordinary skill in the art.

In one embodiment, the second ion implantation regions 443 a′ and 443 b′ may be deeper than, and wider than, the first ion implantation regions 441 a′ and 441 b′. It is known that the diffusivity of B⁺ ions within the substrate 420 is approximately five times higher than that of BF₂ ⁺ ions. Therefore, with the same ion implantation energy, a region implanted with B⁺ ions can be formed deeper and wider than a region implanted with BF₂ ⁺.

Referring to FIG. 6D, second ion implantation masks M2 are formed on an off-cell region of the mask ROM region and a PMOS region of the CMOS region and a third ion implantation process is performed to form third ion implantation regions 445 a′ and 445 n′.

The third ion implantation regions 445 a′ and 445 n′ may be regions implanted with N-type ions or regions having a low concentration of implanted ions in a well-known LDD junction.

The third ion implantation regions 445 a′ and 445 n′ may be formed deeper and wider than the first ion implantation region 441 a′, and may be formed shallower and narrower than the second ion implantation region 443 a′.

Referring to FIG. 6E, a third ion implantation mask M3 exposing only the PMOS region of the CMOS region is formed and a fourth ion implantation process is performed to form a fourth ion implantation region 445 p′. The fourth ion implantation region 445 p′ corresponds to a lightly ion-implanted region in an LDD junction of the PMOS region.

Referring to FIG. 6F, gate spacers 439 a through 439 d are formed on the gate electrodes 433 a through 433 d, respectively.

In one embodiment, the gate spacers 439 a through 439 d are formed on the gate electrodes 433 a through 433 d, respectively, by forming an insulating film (e.g., comprising silicon nitride, silicon oxynitride, or the like or a combination thereof) on the gate insulating film 431 a′, gate capping layers 435 a through 435 d, and gate sidewalls 437 a through 437 d followed by anisotropically etching the insulating film. Since the anisotropic etching method is a well-known technology, a detailed description thereof will be omitted.

Referring to FIG. 6G, a fourth ion implantation mask M4 is formed on the PMOS region of the CMOS region and a fifth ion implantation process is performed to form fifth ion implantation regions 447 a′, 447 b, and 447 n′. The first through fourth ion implantation regions 441 a′ and 441 b′, 443 a′ and 443 b′, 445 a′ and 445 n′, and 445 p′ are aligned with the gate electrodes 433 a through 433 d or with gate sidewalls 437 a through 437 d. The fifth ion implantation regions 447 a′, 447 b′ and 447 n′ are aligned with the gate spacers 439 a through 439 c.

In the illustrated embodiments, the fifth ion implantation regions 447 a′, 447 b′ and 447 n′ may be deeper than the first through fourth ion implantation regions 441 a′ and 441 b′, 443 a′ and 443 b′, 445 a′ and 445 n′, and 445 p′.

The ion implantation processes described above with reference to FIGS. 6D through 6G may be understood based on a process of forming an LDD junction of the PMOS region and a process of forming an LDD junction of the NMOS region. Since a technology of forming an LDD junction is well known, a detailed description thereof will be omitted.

Referring to FIG. 6H, a fifth ion implantation mask M5 exposing the PMOS region of the CMOS region is formed. Then, a sixth ion implantation process is performed to form a sixth ion implantation region 447 p′.

The sixth ion implantation region 447 p′ is aligned with the gate spacer 439 d of the PMOS region.

The sixth ion implantation region 447 p′ corresponds to a lightly ion-implanted region in the LDD junction of the PMOS region.

Referring to FIG. 6I, junction structures 440 a through 440 d are formed in transistor structures of the mask ROM region and the CMOS region, respectively.

In FIG. 6I, the ion implantation regions in each of the junction structures 440 a through 440 d appear distinct from one another. It will be appreciated, however, that these ion implantation regions they may appear to be a single region.

After the above ion implantation processes, a heat-treatment process may be performed to diffuse the implanted ions. Consequently, a recombination or depletion region may be formed. Accordingly, each ion implantation region may be diffused and expand under each of gate structures 430 a through 430 d and into the substrate.

As exemplarily described above, an on-cell transistor structure of a mask ROM device can maintain a low leakage current and a sufficiently high breakdown voltage. Because no channel is formed even when an off-cell transistor is activated, the off-cell can stably output data. Such a mask ROM can be simply fabricated without separate photolithography processes by replacing an ion implantation source. A semiconductor device including such a mask ROM device can execute commands and operate in a stable manner, thereby increasing yields.

According to an embodiment, there is provided a mask ROM device. The mask ROM device includes an on-cell having an on-cell gate structure, which includes an on-cell gate insulating film, an on-cell gate electrode and an on-cell gate spacer formed on a substrate, and an on-cell junction structure, which includes, within the substrate, first and second on-cell ion implantation regions of a first polarity and third and fourth on-cell ion implantation regions of a second polarity; and an off-cell having an off-cell gate structure, which includes an off-cell gate insulating film, an off-cell gate electrode and an off-cell gate spacer formed on the substrate, and an off-cell junction structure, which includes, within the substrate, first and second off-cell ion implantation regions of the first polarity and a third off-cell ion implantation region of the second polarity.

According to another embodiment, there is provided a method of fabricating a mask ROM device. The method includes forming an on-cell gate insulating film and an off-cell gate insulating film on a substrate, forming an on-cell gate electrode on the on-cell gate insulating film and forming an off-cell gate electrode on the off-cell gate insulating film, performing a first ion implantation process and a second ion implantation process using ions of a first polarity to form a first on-cell ion implantation region, a first off-cell ion implantation region, a second on-cell ion implantation region and a second off-cell ion implantation region to be aligned with side surfaces of the on-cell gate electrode and the off-cell gate electrode, performing a third ion implantation process using ions of a second polarity and forming a third on-cell ion implantation region to be aligned with the side surfaces of the on-cell gate electrode and the off-cell gate electrode, forming gate spacers on the side surfaces of the on-cell gate electrode and the off-cell gate electrode, and performing a fourth ion implantation process and forming a fourth on-cell ion implantation region and a third off-cell ion implantation region to be aligned with the gate spacers.

According to another embodiment, there is provided a semiconductor device. The semiconductor device includes a mask ROM device including, an on-cell, which has an on-cell gate structure on a substrate and an on-cell junction structure in the substrate, and an off-cell which has an off-cell gate structure on the substrate and an off-cell junction structure in the substrate, and a CMOS including, a PMOS gate structure, which comprises a PMOS gate insulating film, a PMOS gate electrode and a PMOS gate spacer formed on a second region of the substrate, a PMOS structure, which comprises a P-type ion implantation region formed within the second region of the substrate, an NMOS gate structure, which comprises an NMOS gate insulating film, an NMOS gate electrode and an NMOS gate spacer formed on the second region of the substrate, and an NMOS structure which comprises an N-type ion implantation region formed within the second region of the substrate, wherein the on-cell gate structure includes an on-cell gate insulating film, an on-cell gate electrode and an on-cell gate spacer formed on a first region of the substrate, an on-cell junction structure includes, within the first region of the substrate, first and second on-cell ion implantation regions of a first polarity and third and fourth on-cell ion implantation regions of a second polarity, an off-cell gate structure includes an off-cell gate insulating film, an off-cell gate electrode and an off-cell gate spacer formed on the first region of the substrate, and an off-cell junction structure includes, within the first region of the substrate, first and second off-cell ion implantation regions of the first polarity and a third off-cell ion implantation region of the second polarity.

According to another embodiment, there is provided a method of fabricating a semiconductor device. The method includes forming an on-cell gate insulating film and an off-cell gate insulating film on a first region of a substrate and forming a CMOS gate insulating film on a second region of the substrate, forming an on-cell gate electrode on the on-cell gate insulating film, forming an off-cell gate electrode on the off-cell gate insulating film, and forming CMOS gate electrodes, which comprise an NMOS gate electrode and a PMOS gate electrode, on the CMOS gate insulating film, performing a first ion implantation process and a second ion implantation process using ions of a first polarity and forming a first on-cell ion implantation region, a first off-cell ion implantation region, a second on-cell ion implantation region and a second off-cell ion implantation region to be aligned with side surfaces of the on-cell gate electrode and the off-cell gate electrode, performing a third ion implantation process using ions of a second polarity and forming a third on-cell ion implantation region and a first NMOS ion implantation region to be aligned with side surfaces of the on-cell gate electrode and the NMOS gate electrode, performing a fourth ion implantation process using ions of the first polarity and forming a first PMOS ion implantation region to be aligned with a side surface of the PMOS gate electrode, forming an on-cell gate spacer, an off-cell gate spacer, an NMOS gate spacer and a PMOS gate spacer on the side surfaces of the on-cell and off-cell gate electrodes and the NMOS and PMOS gate electrodes, respectively, performing a fifth ion implantation process using ions of the second polarity and forming a fourth on-cell ion implantation region, a third off-cell ion implantation region and a second NMOS ion implantation region to be aligned with the on-cell gate spacer, the off-cell gate spacer and the NMOS gate spacer; and performing a sixth ion implantation region using ions of the first polarity and forming a second PMOS ion implantation region to be aligned with the PMOS gate spacer.

While exemplary embodiments have been shown and described above, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. The exemplary embodiments should be considered in descriptive sense only and not for purposes of limitation. 

1. A method of fabricating a mask ROM device, the method comprising: forming an on-cell gate insulating film and an off-cell gate insulating film on a substrate; forming an on-cell gate electrode on the on-cell gate insulating film; forming an off-cell gate electrode on the off-cell gate insulating film; performing a first ion implantation process and a second ion implantation process using ions of a first polarity to form a first on-cell ion implantation region, a first off-cell ion implantation region, a second on-cell ion implantation region and a second off-cell ion implantation region, wherein the first and second on-cell ion implantation regions are aligned with a side surface of the on-cell gate electrode and wherein the first and second off-cell ion implantation regions are aligned with a side surface of the off-cell gate electrode; performing a third ion implantation process using ions of a second polarity to form a third on-cell ion implantation region that is aligned with the side surfaces of the on-cell gate electrode and the off-cell gate electrode; forming gate spacers on the side surfaces of the on-cell gate electrode and the off-cell gate electrode; and performing a fourth ion implantation process to form a fourth on-cell ion implantation region and a third off-cell ion implantation region that are aligned with the gate spacers.
 2. The method of claim 1, wherein the first on-cell ion implantation region and the first off-cell ion implantation region are formed by implanting boron fluoride ions, and the second on-cell ion implantation region and the second off-cell ion implantation region are formed by implanting boron ions.
 3. The method of claim 1, wherein the first on-cell ion implantation region and the first on-cell ion implantation region are formed by implanting ions into the substrate in a direction perpendicular to the substrate, and the second on-cell ion implantation region and the second off-cell ion implantation region are formed by implanting ions into the substrate at an angle less than approximately 45 degrees with respect to the substrate.
 4. The method of claim 1, wherein the first and third on-cell ion implantation regions and the first off-cell ion implantation region are aligned with the side surfaces of the on-cell gate electrode and the off-cell gate electrode, and the fourth on-cell ion implantation region and the third off-cell ion implantation region are aligned with the gate spacers.
 5. The method of claim 1, wherein the first on-cell ion implantation region and the first off-cell ion implantation region are formed simultaneously, the second on-cell ion implantation region and the second off-cell ion implantation region are formed simultaneously, and the fourth on-cell ion implantation region and the third off-cell ion implantation region are formed simultaneously.
 6. The method of claim 1, wherein the first and second on-cell ion implantation regions and the first and second off-cell ion implantation regions have the same concentration of implanted ions.
 7. A method of fabricating a semiconductor device, the method comprising: forming an on-cell gate insulating film and an off-cell gate insulating film on a first region of a substrate and forming a CMOS gate insulating film on a second region of the substrate; forming an on-cell gate electrode on the on-cell gate insulating film; forming an off-cell gate electrode on the off-cell gate insulating film; forming an NMOS gate electrode and a PMOS gate electrode on the CMOS gate insulating film; performing a first ion implantation process and a second ion implantation process using ions of a first polarity to form a first on-cell ion implantation region, a first off-cell ion implantation region, a second on-cell ion implantation region and a second off-cell ion implantation region that are aligned with side surfaces of the on-cell gate electrode and the off-cell gate electrode; performing a third ion implantation process using ions of a second polarity to form a third on-cell ion implantation region and a first NMOS ion implantation region that are aligned with side surfaces of the on-cell gate electrode and the NMOS gate electrode, respectively; performing a fourth ion implantation process using ions of the first polarity to form a first PMOS ion implantation region that is aligned with a side surface of the PMOS gate electrode; forming an on-cell gate spacer, an off-cell gate spacer, an NMOS gate spacer and a PMOS gate spacer on the side surfaces of the on-cell and off-cell gate electrodes and the NMOS and PMOS gate electrodes, respectively; performing a fifth ion implantation process using ions of the second polarity to form a fourth on-cell ion implantation region, a third off-cell ion implantation region and a second NMOS ion implantation region that are aligned with the on-cell gate spacer, the off-cell gate spacer and the NMOS gate spacer, respectively; and performing a sixth ion implantation region using ions of the first polarity to form a second PMOS ion implantation region that is aligned with the PMOS gate spacer. 